Spectroscopic and structural characterization of noninnocent mixed-ligand oxidovanadium(V) complexes

Abstract

The reaction between [V IVO(acac)(L)] and the potentially noninnocent ligands catechol (H 2cat/cat 2-) and benzohydroxamic acid (H 2bha/bha 2-), where HL = Hpydx-aebmz, Hpydx-dmen, Hpydx-aepy [ONN donor Schiff bases obtained by condensation of pyridoxal and 2-(2-aminoethyl)benzimidazole (Hpydx-aebmz), 2-(2-aminoethyl)pyridine (Hpydx-aepy), or N,N-dimethylethylenediamine (Hpydx-dmen)], or HL = Hpan [1-(2-pyridylazo)-2-naphthol], in equimolar amounts results in the formation of the distorted octahedral complexes [V VO(cat)(L)] and [V VO(bha)(L)]. The molecular structure of [VO(bha)(pydx-dmen)] is determined by single-crystal X-ray diffraction and confirms the distorted octahedral geometry as well as the ONN and OO binding modes of pydx-dmen - and bha 2-, respectively, in their binding to the V VO centre. The noninnocent catechol 2- and bha 2- ligands play significant roles in the electronic properties of the metal complexes investigated by UV/Vis, IR, and 51V NMR spectroscopy. Evidence for the noninnocent behavior of catechol 2- and bha 2- ligands was obtained; the [V VO(cat)(L)] and [V VO(bha)(L)] complexes exhibit 51V NMR resonances (δ V) in the range +535 to -10 ppm and intense ligand-to-metal charge-transfer bands in the visible and near infrared range. The observed δ V chemical shifts linearly correlate with the inverse of the energies of the LMCT transitions. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.